1. Field of the Invention
The present invention relates to a sensor or sensor configured to experience resistance changes in response to an external interaction.
The present application also relates to a method of constructing a sensing device for sensing an external interaction by effecting a change in resistance.
2. Description of the Related Art
A sensor configured to experience resistance changes in response to an external interaction is disclosed in U.S. Pat. No. 6,501,465, assigned to the present assignee. The disclosed sensor deploys conductive fabric layers and increasing applied pressure results in a greater degree of conductivity between the layers such that the resistance of the connection may be measured in order to determine the degree of applied pressure. An acknowledged problem with systems of this type is that they exhibit a wide range of responses such that it is difficult to predict the way in which resistance will change and it is therefore difficult to engineer the sensor for a particular application.
An alternative approach is disclosed in U.S. Pat. No. 6,291,568, assigned to the present assignee, in which a quantum tunnelling composite (manufactured by the present applicant) is deployed as a material with variable resistivity in response to applied pressure. By using a quantum tunnelling composite, it is possible to control the response of the sensor more accurately, although in some configurations the response may be very sensitive to relatively small pressures or it may have an extended range while being less sensitive to an initial press.
There are two known methods for measuring a change in resistance. One way is to have an electrode at the top with a second electrode at the bottom and pressure sensing material sandwiched in between. A voltage is applied and changes in current are detected due to varying changes in resistance.
An alternative method is to have alternate electrodes on the bottom, referred to as interdigitated fingers, with the pressure sensitive material on the top. These known methods produce different force/resistance profiles because the first method defines one resistance while the second method provides two. Different paths are taken and accordingly there is a different resistance profile.